The present invention generally relates to an auxiliary power supply apparatus capable of supplying electric power to electronic appliances during an interruption of the electric power. More specifically, the present invention is directed to a compact auxiliary (spare) power supply apparatus capable of supplying electric power in a high efficiency.
In general, as represented in FIG. 1, a transformer type power supply circuit is conventionally employed in an electric appliance adapted to the commercial AC power supply. Very recently, a switching type power supply circuit as shown in FIG. 2 is usually employed, since this switching type power supply circuit can be made compact and in light weight.
In an electronic appliance 10T of the transformer type power supply as indicated in FIG. 1, an AC plug 11 is connected via a power supply switch 13 to a primary winding 12p of a power supply transformer 12, anodes of rectifier diodes D1 and D2 are connected to both ends of a secondary winding 12s, and a center tap of the secondary winding 12s is connected to the ground. A cathode of the rectifier diode D1 is commonly connected to a cathode of the rectifier diode D2. A smoothing capacitor Cl is connected between the commonly-connected cathodes and ground, and also an electronic circuit 19 indicated in the form of a resistor is connected between the commonly-connected cathodes and ground.
In the electronic appliance 10T of FIG. 1, when the AC plug 11 is inserted into a plug socket (not shown) of the commercial AC power supply, and the power supply switch 13 is turned ON, an AC voltage having a predetermined value, which is induced between the secondary winding 12s of the power supply transformer 12, is rectified by the diodes D1 and D2 in the full wave mode, so that a DC voltage having a preselected value is applied to the electronic circuit 19.
On the other hand, in an electronic appliance 10S of the switching type power supply, as represented in FIG. 2, an output terminal of a negative polarity side of a diode bridge 14 connected via the power supply switch 13 to the AC plug 11 is connected to the ground. Both one end of a smoothing capacitor C2, and one end of a primary winding 15p of a switching transformer 15 are connected to another output terminal of a positive polarity side of the diode bridge 14. The other end of the capacitor C2 is connected to ground, and further both a source-to-drain path of a field-effect transistor (FET) 16, and a cathode-to-anode of a diode D3 are parallel-connected between the other end of the primary winding 15p and ground. Also, the output from a PWM signal generating circuit 17 is supplied to a gate of the field-effect transistor 16.
An anode of a rectifier diode D4 is connected to one end of a secondary winding 15s of the switching transformer 15, and the other end of the secondary winding 15s is connected to ground. A smoothing capacitor C3 is connected between a cathode of the rectifier diode D4 and the ground, and also the electronic circuit 19 indicated in the form of the resistor is connected between them.
It should be noted that an initiation processing circuit 18 for initiating the PWM signal generating circuit 17 is employed. This initiation processing circuit 18 supplies the DC output of the diode bridge 14 via, for instance, a resistor having a proper value, to the PWM signal generating circuit 17. Additionally, this initiation processing circuit 18 performs the known initiation process, namely, since the DC output derived from the diode bridge 14 is supplied to this initiation processing circuit 18, the PWM signal generating circuit 17 is initiated, and thereafter, the initiation processing circuit 18 rectifies an output of a third winding provided with the switching transformer 15, and switches the DC output of the diode bridge 14 to this rectified output, so that the rectified output of the third winding is supplied.
In the electronic appliances 10S of FIG. 2, when the AC plug 11 is inserted into a plug socket (not shown in detail) of the commercial AC power supply, if the power switch 13 is turned ON, then the commercial AC is directly rectified in the full wave mode by the diode bridge 14. For example, when the voltage of the commercial AC is 100V, this AC voltage is converted into a DC voltage having approximately 140V under peak condition, and a DC voltage having approximately 120V under loaded condition. This DC voltage is applied via the primary winding 15p of the switching transformer 15 to the drain of the field-effect transistor 16 whose source is grounded. At the same time, the PWM signal derived from the PWM signal generating circuit 17 is supplied to the gate of this field effect transistor 16, so that a drain current is interrupted, the PWM signal having a predetermined voltage, which is induced across the secondary winding 15s of the switching transformer 15, is rectified in a half-wave mode by the diode D4, and thus a DC voltage having a preselected value is applied to the electronic circuit 19.
When a power interruption happens to occur in the commercial AC power supply, the electronic appliances 10T and 10S equipped with the power supply circuits adapted to the commercial AC power supply as indicated in FIG. 1 and FIG. 2 cannot be used. Therefore, conventionally, a DC-to-AC type auxiliary (spare) power supply apparatus 20 as indicated in FIG. 3 is utilized in order to be prepared for unpredictable power interruption.
In the auxiliary power supply apparatus 20 of FIG. 3, a dual-polarity/dual-switch (2-circuit/2-contact) type selection switch 23 is interposed between an AC plug 21 and a plug socket type output connector 22, fixed contacts on a side "a" of this selection switch 23 and a side "d" thereof are connected to the AC plug 21, and further movable contacts on a side "c" of this selection switch 23 and a side "f" thereof are connected to an output connector 22.
Also, a DC voltage derived from a cell 24 is converted by a DC/AC inverter 25 into an auxiliary AC voltage of, for instance, 100V in 50 Hz, or 60 Hz, and this auxiliary AC voltage is applied to the fixed contacts (side "b" and side "e") of the switch 23.
Then, a power-interrupt detecting circuit 26 is connected to the AC plug 21, and also an output from this power-interrupt detecting circuit 26 is supplied as a control signal for an initiation operation and a switching operation to the DC/AC inverter 25 and the selection switch 23.
It should also be noted that as the cell 24, for example, a secondary battery having a specification of approximately 6V - 2 Ah is employed with respect to a load in a 5-W class, and is properly charged by a charging circuit 27.
Normally, in the auxiliary power supply apparatus 20 of FIG. 3, the selection switch 23 is connected as indicated by a solid line. Thus, the commercial AC power is conducted from the AC plug 21 to the output connector 22, and then is supplied to the electronic appliance as indicated in FIG. 1, or FIG. 2, which is connected to this output connector 22.
When a power interruption happens to occur in the commercial AC power supply, the selection switch 23 is switched as indicated by a dotted line, and also the DC/AC inverter 25 is initiated in response to the output from the power-interrupt circuit 26. As a result, the auxiliary AC power derived from the DC/AC inverter 25 is conducted to the electronic appliance connected to this output connector 22. As a consequence, the normal operations of these electronic appliances can be maintained even when the power interruption happens to occur.
The DC/AC inverter 25 is mounted on the auxiliary power supply apparatus 20 shown in FIG. 3, which is capable of outputting the AC power for the auxiliary purposes to any one of the electronic appliance 10T equipped with the transformer type power supply, as indicated in FIG. 1, and also of the electronic appliance 10S equipped with the switching type power supply, as represented in FIG. 2.
However, since the operation frequency of this DC/AC inverter 25 is equal to the frequency of the commercial AC power supply, i.e., 50 Hz, or 60 Hz, there is a problem that the efficiency of this DC/AC inverter 25 is lowered, and further the dimension of this DC/AC inverter 25 is increased.
To solve only this efficiency problem, the following solution may be conceived. That is, both a DC/AC inverter adaptable to an electronic appliance of a transformer type power supply and a DC/DC converter adaptable for an electronic appliance of a switching type power supply are mounted on an auxiliary power supply apparatus, and then any one of these DC/AC inverter and DC/DC converter may be selectively used in accordance with a type of a power supply circuit for a load set. However, this solution owns another problem that such a conceived auxiliary power supply apparatus would become bulky, and would have a cost problem.